Investigation on partially replacing metakaolin with marine shell waste to produce sustainable eco-friendly geopolymer mortars

Abstract

This work focuses on the effect of the incorporation of marine shell waste in different mass substitution rates in geopolymer mortars as an efficient solution to overcome the problems related to this waste. In this paper, Lebanese metakaolin was used as the primary clay source of aluminosilicate for the geopolymer mortars. Then, a mass substitution of metakaolin with shell waste was drawn in terms of structure, synthesis mechanism, and parameters delimiting their performance. The chemical properties of all constituents were investigated using X-ray diffraction analysis and X-ray Fluorescence. Also, the microstructure analysis was observed by implementing a scanning electron microscope (SEM). The compressive strength and elasticity modulus were measured as two fundamental mechanical properties of geopolymer samples by highlighting the impact of curing conditions (non-heated and heated) after passing 1, 3, 7, 28, 90, 120, 180, and 360 days and the various substitution rates (0–20%). The results showed that the curing conditions and the various substitution rates of metakaolin with marine shells affected the microstructure and mechanical properties. Adding shell waste reduced the compressive strength for both non-heated and heated samples and slightly increased the elasticity modulus up to 10% for non-heated and for heated curing conditions. While the final compressive strengths of non-heated samples are greater than heated ones, the rate of achieving a specific compressive strength is more rapid for heated samples. An environmental and economic analysis showed that assuming an equal transportation cost, replacing metakaolin with an average amount of 10% seashell waste reduces the energy usage by 7% and the price by 2% to produce 1 ton of geopolymer and preserves the non-renewable sources of Kaolin clay and solves the problems related to seashell waste deposits.